System and methods for distribution of heterogeneous wavelength multiplexed signals over optical access network

ABSTRACT

An optical network communication system includes an optical hub, an optical distribution center, at least one fiber segment, and at least two end users. The optical hub includes an intelligent configuration unit configured to monitor and multiplex at least two different optical signals into a single multiplexed heterogeneous signal. The optical distribution center is configured to individually separate the at least two different optical signals from the multiplexed heterogeneous signal. The at least one fiber segment connects the optical hub and the optical distribution center, and is configured to receive the multiplexed heterogeneous signal from the optical hub and distribute the multiplexed heterogeneous signal to the optical distribution center. The at least two end users each include a downstream receiver configured to receive one of the respective separated optical signals from the optical distribution center.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/590,464, filed May 9, 2017, which prior application claims thebenefit of and priority to U.S. Provisional Patent Application Ser. No.62/352,279, filed Jun. 20, 2016, both of which are incorporated hereinby reference in their entireties.

BACKGROUND

The field of the disclosure relates generally to fiber communicationnetworks, and more particularly, to optical access networks utilizingwavelength division multiplexing.

Telecommunications networks include an access network through which enduser subscribers connect to a service provider. Some such networksutilize fiber-optic distribution infrastructures, which havehistorically provided sufficient availability of fiber strands such thatdissimilar types of optical transport signals are carried over their owndifferent fibers. Bandwidth requirements for delivering high-speed dataand video services through the access network, however, is rapidlyincreasing to meet growing consumer demands. As this signal capacitydemand continues to grow, the capacity of individual long access fiberstrands is limited. The cost of installing new long access fibers isexpensive, and dissimilar optical transport signals, unless they arepurposely isolated, experience interference from one another on the samefiber strand. This legacy fiber environment requires operators tosqueeze more capacity out of the existing fiber infrastructure to avoidcosts associated with having to retrench new fiber installment.

Conventional access networks typically include six fibers per node,servicing as many as 500 end users, such as home subscribers, with twoof the fibers being used for downstream and upstream residentialtransport, and the remaining used for node splitting or businessesservices. Conventional nodes cannot be split further using conventionaltechniques, and do not typically contain spare (unused) fibers, and thusthere is a need to utilize the limited fiber availability in a moreefficient and cost-effective manner. Dense Wavelength DivisionMultiplexing (DWDM) environments, for example, are capable ofmultiplexing signals using similar optical transport techniques. Incertain access network environments such as the cable televisionenvironment, DWDM is able to utilize different formats, but its fiberstrand availability is still limited by conventional fiber-opticinfrastructure costs and considerations. Cable access networks includeanalog modulation of the cable RF spectrum onto optical carriers,baseband digital modulation of an optical carrier supporting businessservices, and Ethernet passive optical network (EPON) and Gigabitpassive optical network (GPON) systems carrying data for residential orbusiness subscribers. Each of these different optical transport signalstypically requires its own dedicated long fiber strands.

Coherent technology has been proposed as one solution to meet the everincreasing signal traffic demand for WDM-PON optical access networks, inboth brown and green field deployments, particularly with respect tolong and metropolitan links for achieving high spectral efficiency (SE)and higher data rates per channel. Coherent technology in long opticalsystems typically requires significant use of high quality discretephotonic and electronic components throughout the access network, suchas digital-to-analog converters (DAC), analog-to-digital converters(ADC), and digital signal processing (DSP) circuitry such as anapplication-specific integrated circuit (ASIC) utilizing CMOStechnology, to compensate for noise, drift, and other factors affectingthe transmitted channel signals over the access network. Furthermore, asthe number of end users per optical fiber increases, so does the cost,and power requirements, of implementing all of these electroniccomponents for each terminal device in the network. Some known proposedcoherent solutions have also required their own dedicated long fiberstrands to avoid interference from dissimilar optical transport signals.Accordingly, a solution is desired that allows dissimilar transportsignals to coexist on the same transmission fibers.

BRIEF SUMMARY

In an embodiment, an optical network communication system includes anoptical hub, an optical distribution center, at least one fiber segment,and at least two end users. The optical hub includes an intelligentconfiguration unit configured to monitor and multiplex at least twodifferent optical signals into a single multiplexed heterogeneoussignal. The optical distribution center is configured to individuallyseparate the least two different optical signals from the multiplexedheterogeneous signal. The at least one fiber segment connects theoptical hub and the optical distribution center, and is configured toreceive the multiplexed heterogeneous signal from the optical hub anddistribute the multiplexed heterogeneous signal to the opticaldistribution center. The at least two end users each include adownstream receiver configured to receive one of the respectiveseparated optical signals from the optical distribution center.

In an embodiment, a method of distributing heterogeneous wavelengthsignals over a fiber segment of an optical network is provided. Themethod includes the steps of monitoring at least two different opticalcarriers from at least two different transmitters, respectively,analyzing one or more characteristics of the fiber segment, determiningone or more parameters of the at least two different optical carriers,and assigning a wavelength spectrum to each of the at least twodifferent optical carriers according to the one or more analyzed fibersegment characteristics and the one or more determined optical carrierparameters.

In an embodiment, an optical distribution center apparatus, includes aninput optical interface for communication with an optical hub, an outputoptical interface for communication with one or more end user devicesconfigured to process optical signals, a wavelength filter forseparating a downstream heterogeneous optical signal from the inputoptical interface into a plurality of downstream homogenous opticalsignals, and a downstream optical switch for distributing the pluralityof downstream homogeneous optical signals from the wavelength filter tothe output optical interface in response to a first control signal fromthe optical hub.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIGS. 1A-1C illustrate input signal emission spectra that can beutilized with fiber communication systems in accordance with anexemplary embodiment of the present disclosure.

FIGS. 2A-2C illustrate interaction of multiple signals from differentlongitudinal modes according to the exemplary emission spectrum depictedin FIG. 1C.

FIG. 3 is a schematic illustration of an exemplary fiber communicationsystem in accordance with an embodiment of the present disclosure.

FIG. 4 is a schematic illustration of an exemplary fiber communicationsystem in accordance with an embodiment of the present disclosure.

FIG. 5 is a schematic illustration of an alternative fiber communicationsystem to the embodiment depicted in FIG. 4.

FIGS. 6A-6D illustrate an exemplary successive wavelength placement ofheterogeneous optical signals in accordance with an exemplary embodimentof the present disclosure.

FIG. 7 illustrates an alternative three dimensional wavelength placementof the embodiment depicted in FIG. 6D.

FIG. 8 is a flow chart diagram of an exemplary optical signal wavelengthallocation process.

FIG. 9 is a flow chart diagram of an exemplary fiber segment analysisprocess that can be implemented with the allocation process depicted inFIG. 8.

FIGS. 10A-C illustrate a flow chart diagram of an exemplary signalanalysis process that can be implemented with the allocation processdepicted in FIG. 8.

FIG. 11 is a flow chart diagram of an exemplary spectrum assignmentprocess that can be implemented with the allocation process depicted inFIG. 8.

FIG. 12 illustrates an alternative hybrid optical distribution centerthat can be implemented with the fiber communication systems depicted inFIGS. 3-5.

Unless otherwise indicated, the drawings provided herein are meant toillustrate features of embodiments of this disclosure. These featuresare believed to be applicable in a wide variety of systems including oneor more embodiments of this disclosure. As such, the drawings are notmeant to include all conventional features known by those of ordinaryskill in the art to be required for the practice of the embodimentsdisclosed herein.

DETAILED DESCRIPTION

In the following specification and the claims, reference will be made toa number of terms, which shall be defined to have the followingmeanings.

The singular forms “a,” “an,” and “the” include plural references unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about,” “approximately,” and “substantially,” are notto be limited to the precise value specified. In at least someinstances, the approximating language may correspond to the precision ofan instrument for measuring the value. Here and throughout thespecification and claims, range limitations may be combined and/orinterchanged; such ranges are identified and include all the sub-rangescontained therein unless context or language indicates otherwise.

According to the embodiments herein, an optical distribution system iscapable of optimally carrying and multiplexing a plurality ofheterogeneous optical transport signals. The present embodiments mayfurther be advantageously implemented with both new and legacydistribution networks so significantly improve both capacity andperformance of such systems.

Optical signals consume different amounts of fiber resources dependingon their respective power levels, modulation formats, and wavelengththey occupy in relation to wavelengths and characteristics ofneighboring signals, symbols and/or bandwidths, among other parameters.The systems described herein implement hardware and algorithms toaggregate and configure multiple different optical signals within thesame optical fiber. The embodiments herein further utilize disclosurealso introduces relations between performance metrics, optical signalconfiguration parameters and fiber capability for carrying these opticalsignals.

FIGS. 1A-1C illustrate approximate signal emission spectra that can beutilized with fiber communication systems in accordance with anexemplary embodiment of the present disclosure. Referring now to FIG.1A, an emission spectrum 100 for an LED (Light Emitting Diode, notshown) is illustrated. Emission spectrum 100 represents power 102(y-axis) against wavelength 104 (x-axis) for emitted light 106. Laserdiodes are implemented from a semiconductor junction operated in forwardbias mode. Electrons in that junction transition from a higher to alower energy state. In such a process, a photon that has an energy equalto the difference in energy states of the electron is emitted, whichrepresents the spontaneous emission of light present in an LED, asillustrated in FIG. 1A.

Referring now to FIG. 1B, an emission spectrum 108 is illustrated for alaser diode such as a Fabry Perot laser diode (FPLD) or avertical-cavity surface-emitting laser (VCSEL). Such laser diodes mayalso implement reflective facets or mirrors so that generated photonsbounce back and forth stimulating, along their path, the emission ofmore photons. This stimulated emission, or lasing, results in lightemission at higher intensity levels and with a high degree of coherence.The mirror or facets on opposite sides of the active region formed bythe junction create an optical cavity. The geometry of that cavity alongwith the range in energy levels generated by the change of state in thejunction will determine one or more dominant resonant wavelengthstransmitted by the laser diode.

In an exemplary embodiment, an FPLD may have an optical bandwidth of 5to 10 nanometers (nm), and generate a plurality of individuallongitudinal modes 110, each having an output bandwidth typically lessthan 2 nm. In an embodiment, an 850 nm laser diode with a length ofaround 300 micrometers (μm) and a refractive index of approximately 4may have a longitudinal mode spacing of 0.3 nm, which is similar to a 1mm long 1550 nm laser diode. Changing the length or refractive index ofthe cavity, for example by heating or cooling the laser diode, may shiftthe whole comb of modes and consequently the output wavelength.

Referring now to FIG. 1C, an emission spectrum 112 is illustrated for alaser diode such as a distributed feedback laser diode (DFBLD). In anoptical signal source, the dominant lasing wavelength is dependent onthe material which provides a broad wavelength range that generateslight based on the band-gap between electron states of a semiconductorjunction, as well as the length of the cavity which results in amultitude of resonant modes that restricts the wavelengths. The dominantlasing wavelength is further dependent on structural characteristics ofthe cavity that further restrict resonance to a single longitudinal mode114, while suppressing adjacent longitudinal modes 116. A DFBLD, througha periodic index of refraction variation, is capable of thus limitingresonance substantially to a single wavelength, i.e., longitudinal mode114, as illustrated in FIG. 1C.

According to the embodiments described herein, and further below,sources include LEDs, FPLDs, VCSELs, and DFBLDs. One of ordinary skillin the art though, after reading and comprehending the presentdisclosure, will understand that other sources may be implementedwithout departing from the scope of the application. The sourcesdescribed herein are capable of converting electrical signals intooptical signals, and can be significantly different devicesstructurally. In an exemplary embodiment, the lasing source can bemanufactured on semiconductor devices/chips. LEDs and VCSELs, forexample, may be fabricated on semiconductor wafers such that light isemitted from the surface of the chip. FPLDs may be fabricated such thatlight is emitted from the side of the chip from a laser cavity createdin the middle of the chip.

LEDs are the least expensive source, but produce lower power outputsthan most of the other optical sources. LEDs also produce a larger,diverging light output pattern (see FIG. 1A, above), which reduces theapplications available to couple LEDs into fibers. LEDs and VCSELsthough, are generally inexpensive to manufacture in comparison with theother sources described herein. FPLDs and DFBLDs, for example, are moreexpensive to manufacture due to the necessity of creating the lasercavity inside the device, however, the output light from such sourcesare narrower and more easily coupled to single mode fibers.

DFBLDs have narrower spectral width than FPLDs, which realizes lesschromatic dispersion on longer fiber links. DFBLDs are more expensive tomanufacture than FPLDs, but also produce a more highly linear output,that is, the light output directly follows the electrical input, and maybe preferable as sources in AM CATV systems and long distance and DWDMsystems. According to the embodiments described below, many of thesesources can be utilized alternatively and/or together according to theadvantageous structural configurations described below.

FIGS. 2A-2C illustrate interaction of multiple signals from differentlongitudinal modes according to the exemplary emission spectrum depictedin FIG. 1C. In a fiber optic distribution system, there are manypotential sources for non-linear behavior. One known source ofnon-linear behavior is an optical amplifier, such as an erbium-dopedfiber amplifier (EDFA). However, even when no amplifiers are present,fiber non-linearities can also impact performance, such as fromcross-phase modulation (CPM), self-phase modulation (SPM), and/orfour-wave mixing (FWM) which originate when the index of refractionchanges with optical power.

Referring now to FIG. 2A, an emission spectrum 200 is illustrated for afirst signal source (not shown) generating a first dominant longitudinalmode 202, and suppressing first adjacent longitudinal modes 204. FIG.2B, illustrates a emission spectrum 206 is illustrated for a secondsignal source (not shown) generating a second dominant longitudinal mode208, and suppressing second adjacent longitudinal modes 210. In anexemplary embodiment, first and second signal sources are heterogeneouswith respect to one another. FIG. 2C represents the superpositionemission spectrum 212 of first and second signal sources together.

Referring now to FIG. 2C, one type of a non-linear effect is illustratedto depict intermodulation between adjacent carriers. In this example,first dominant longitudinal mode 202 and second dominant longitudinalmode 208, along with their respective suppressed first adjacentlongitudinal modes 204 and second adjacent longitudinal modes 210, arespaced apart along the wavelength spectrum, such as may occur with firstand second signals are intermodulated over the same fiber. In thisexample, the simultaneous transmission of the two signals on the samefiber produces noise artifacts 214 within the spectra of adjacentlongitudinal modes 204, 210. Noise artifacts 214(1) and 214(2) includenon-linear components resulting from the interference of the first andsecond signals. Noise artifacts 214 are more difficult to manage wherethe first and second signals are heterogeneous and not filtered.

Additionally, as different parameters, such as temperature, current,modulation bandwidth, and others change, the lasing wavelength of therespective signal may shift, or a different lasing mode may becomedominant, thereby further increasing the likelihood and significance ofnoise artifacts 214 in operation. For these reasons, conventionalsystems do not transmit heterogeneous signals over the same fibers.According to the systems and methods disclosed herein, on the otherhand, a plurality of heterogeneous optical signals, carried overdifferent wavelengths, are transmitted through a single fiber, bymanaging and mitigating the interference problems that would beotherwise experienced by conventional communication networks.

FIG. 3 is a schematic illustration of an exemplary fiber communicationsystem 300 implementing the principles described above with respect toFIGS. 1 and 2. System 300 includes an optical hub 302, an opticaldistribution center (ODC) 304, deep nodes 306, and end users 308. Endusers 308 are one or more downstream termination units, which can be,for example, a customer device or customer premises 308(1) (e.g., ahome, apartment building, or residential radio frequency over glass(RFoG) subscribers), a business user 308(2) (including point tomultipoint fiber networks with business EPON subscribers), an opticalnetwork unit (ONU, not shown), or a cellular base station 308(3)(including small cell base stations). Optical hub 302 is, for example, acentral office, a communications hub, or an optical line terminal (OLT).In an exemplary embodiment, system 100 utilizes a passive opticalnetwork (PON) and coherent Dense Wavelength Division Multiplexing (DWDM)PON architecture. ODC 304 may be separate from deep nodes 306, or mayinclude a hybrid architecture (see FIG. 12) that includes at least onedeep node within the same ODC apparatus structure.

Optical hub 302 communicates with optical distribution center 304 by wayof long fiber 310. In an exemplary embodiment, long fiber 310 istypically around 30 kilometers (km) in length, but may vary, asdescribed below. However, according to the embodiments presented herein,greater lengths are contemplated, such as between 100 km and 300 km, andup to 1000 km. Optionally, long fiber 310 may be two separate fibersseparately dedicated to downstream and upstream communication,respectively.

In an exemplary embodiment, optical distribution center 304 connectswith end users 308 directly through short fibers 312, coaxial cable 314,and/or indirectly through intervening deep nodes 306. Signal power overcoaxial cable 314 may be boosted by amplifiers 316 located along thecable path. In an exemplary embodiment, an individual short fiber 312spans a distance typically less than 5000 feet.

In this example, fiber communication system 300 represents a cableaccess network, which may span distances ranging from 5 km to 140 km.Over this range, signal behaviors that depend on the time of interaction(common distance) are a consideration. Such behaviors may include fibernon-linear effects, dispersion, among others. Typical access networksmay split a single fiber into many subpaths, which can result in asignificant power loss (e.g., up to 18 decibel (dB) loss for a 32-waysplit) along the subpaths. The low robustness signal characteristic canfurther render some signal types more susceptible to noise generated byadjacent signals, as well as optical carriers exhibiting higher power.

To address these issues, optical hub 302 further includes an intelligentconfiguration unit 318 and at least one transmitter 320. Optionally,where upstream communication is desired, optical hub 302 furtherincludes at least one receiver 322. Intelligent configuration unit 318further includes a processor 324 and a signal multiplexer 326. Asdescribed further below with respect to FIGS. 6-11, processor 324functions to analyze and aggregate a plurality of heterogeneous opticalsignals along an optimum spectrum distribution for transmission bymultiplexer 326 over the same long fiber 310.

Intelligent configuration unit 318 operates to analyze (i.e., byprocessor 324) and aggregate (i.e., by multiplexer 326) a plurality ofheterogeneous signals by measuring and controlling one or more of thefollowing parameters: signal wavelength; optical power; modulationformat; modulation bandwidth; polarization multiplexing; channelcoding/decoding, including forward error correction, and fiber length.Intelligent configuration unit 318 is thus able to maximize the capacityof long fiber 310 to transmit multiple heterogeneous signals to ODC 304,where the multiplexed heterogeneous signals can be demultiplexed andseparately transmitted to individual hybrid fiber-coaxial (HFC) opticalnodes, such as deep nodes 306, to an expanding number of end pointswithin the existing HFC node serving area of system 300. In an exemplaryembodiment, these end points may include additional deep nodes 306 insuccession, or cascade, along particular additional signal transmissionpaths that have been generated through successive node splitting inresponse to capacity shortage.

According to the embodiments herein, optical transmission ofheterogeneous signals over existing optical fiber networks significantlyimproves the capacity of existing fibers that only transmit a singleoptical signal. Optical fibers that carry only one optical signal havefew parameters to consider in optimizing performance for that particulartransmission, since there is generally no interaction with other opticalsignals. For single optical signal transmission, considerations forperformance optimization are dependent only on the limitations that thesignal generates onto itself, as well as linear and non-linear factorsof the optical transmission medium.

The simultaneous transmission of multiple heterogeneous optical signals,on the other hand, addresses a variety of different modulation formatsand configuration parameters among the several signals. The presentoptimization scheme additionally selects configuration parameters basedon the performance dependencies that exist between the different opticalsignals, as well as the fiber medium they share.

Intelligent configuration unit 318 functions to multiplex a plurality ofheterogeneous optical signals together according to specific criteria tooptimize quality of signal transmission while minimizing interferencebetween optical signals of different types. Intelligent configurationunit 318 analyzes incoming optical signals of different types (e.g.,analog, direct, coherent, etc.) using processor 324, and multiplexes thesignals together utilizing signal multiplexer 326 so that the differentsignals may coexist over the length of long fiber 310 withoutsubstantially interfering with each other. Intelligent configurationunit 318 works cooperatively with ODC 304 such that ODC 304 maydemultiplex the heterogeneous signal types from one another to beseparately transmitted over short fibers 312 to particular end users 308capable of receiving that type of signal, as illustrated below withrespect to FIGS. 4 and 5.

In an exemplary embodiment, ODC 304 functions as a one-stage opticalfilter to separate the input multiplexed heterogeneous signals fromintelligent configuration unit 318, over long fiber 310, into outputseparate homogeneous signal types over short fibers 312. In thisembodiment, ODC 304 performs as a pure optical-in/optical-out filter. Inan alternative embodiment, ODC 304 is additionally capable of convertingone or more output homogeneous signals into an electrical signaltransmitted over cable 314. Where deep nodes 306 are implemented alongthe signal path, a homogenous signal of a particular carrier type can befiltered by a particular deep node 306 to output a particular bandwidthfor continued transmission to a particular end user 308. Alternatively,fiber deployed from ODC 304 may include direct express fiber runs toeach, or some, of end users 308.

ODC 304 and cascading deep nodes 306 thus a function together as aflexible spectrum filter, with deep nodes 306 tailored to the particularbandwidth desired. In contrast, conventional filtering techniques areknown to drop or add wavelengths onto a fiber loop. The wavelength- andfiber-sharing techniques disclosed herein may thus result incost-effective implementations to reach the end user. Variations andevolved implementations of EPON and GPON systems are also compatiblewith the systems and methods disclosed herein. By this advantageousconfiguration, multiple signals different carrier types effectively“re-use” the same long fiber that would be conventionally dedicated toonly one single signal type, thus eliminating the need to retrench newfibers for the different signal types.

FIGS. 4 and 5 illustrate alternative system implementations to employthe principles described above with respect to FIG. 3. The alternativesystem implementations both are configured to aggregate heterogeneousoptical signals within at least one long fiber each for downstream andupstream transmission, thereby leveraging the fibers presently availablein the optical access environment of cable networks. If more efficientfiber utilization is desired, downstream and upstream transmissions maybe both placed on a single fiber, through utilization of the wavelengthcontrol and management capabilities of intelligent configuration unit318. However, in such instances, the amount of wavelength spectrum perdirection (upstream or downstream) would be reduced in half. In anexemplary embodiment, optical circulators are employed at both ends ofthe fiber link (e.g., systems 300, 400, 500) to further enable thisbidirectional alternative approach over a single fiber. Accordingly,both alternative systems shown in FIGS. 4 and 5, respectively, may bemaintained such that they are kept substantially free of optical beatinterference (OBI free).

In the exemplary alternatives shown in FIGS. 4 and 5, both systems areillustrated to implement cable fiber distribution networks.Nevertheless, a person of ordinary skill in the art, after reading andcomprehending the written description herein and its accompanyingdrawings, will understand to be able to apply the principles andtechniques so disclosed to other types of optical distribution networks,such as cellular distribution networks, digital subscriber line (DSL)based distribution networks, and others.

Referring now to FIG. 4, a schematic illustration of an exemplary fibercommunication system 400 is shown. System 400 is capable of leveragingwavelength tuning capabilities of multiple optical sources. Similar tosystem 300, above, system 400 includes an optical hub 402, an ODC 404,and end users 406. Optical hub 402 communicates with ODC 404 throughdownstream long fiber 408 and optional upstream long fiber 410. ODC 404communicates with end users 406 through short fibers 412. Forsimplification of explanation, deep nodes and cable are not shown, butmay be implemented along the signal path of short fibers 412 in asimilar manner to the embodiments described above with respect to FIG.3.

Optical hub 402 includes a downstream transmitting portion 414 and anoptional upstream receiving portion 416. In an exemplary embodiment,downstream transmitting portion 414 includes at least two of an analogdownstream transmitter 418, an intensity modulated direct detection(IM-DD) downstream transmitter 420, and a coherent downstreamtransmitter 422. End users 406 are comparable to end users 308 (FIG. 3),and may, for example, include one or more downstream termination units.In the exemplary embodiment, end users 406 include at least two of ananalog downstream receiver 424, an IM-DD downstream receiver 426, and acoherent downstream receiver 428.

Where upstream communication is optionally desired (i.e., throughupstream long fiber 410), upstream receiving portion 416 includes atleast two of an analog upstream receiver 430, an IM-DD upstream receiver432, and a coherent upstream receiver 434. In this exemplary embodiment,end users 406 include at least two of an analog upstream transmitter436, an IM-DD upstream transmitter 438, and a coherent upstreamtransmitter 440.

In operation, optical hub 402 further includes an intelligentconfiguration unit 442, comparable to intelligent configuration unit 318(FIG. 3), which analyzes incoming optical signals 444 of different types(e.g., analog optical signal 444(1), IM-DD optical signal 444(2),coherent optical signal 444(3), etc.) and multiplexes the incomingoptical signals 444 together so that the different signals may coexistover the length of long fiber 408 without substantially interfering witheach other. Intelligent configuration unit 442 works cooperatively withODC 404 such that ODC 404 may demultiplex the heterogeneous signal typesfrom one another to be separately transmitted over short fibers 412 toparticular end users 406 capable of receiving that type of signal. Forexample, analog optical signal 444(1) is received by analog downstreamreceiver 424 of end user 406(1), IM-DD optical signal 444(2) is receivedby IM-DD downstream receiver 426 of end user 406(2), and coherentoptical signal 444(3) is received by coherent downstream receiver 428 ofend user 406(3).

In the exemplary embodiment, intelligent configuration unit 442 is asingle intelligent device that also functions to multiplex, aggregate,and combine incoming optical signals 444. In an alternative embodiment,the multiplexing, aggregating, and combining functions may be performedby separate, passive devices (not shown). According to anotheralternative, such separate devices include sufficient intelligencefunctionality such that they are subject to some level of control andmanagement by intelligent configuration unit 446. In some embodiments,intelligent configuration unit 446 is a standalone device that managesand controls separate devices that function to monitor and manipulatesignals, including, for example, lasers that can be configured to usedspecific channels and operate with certain conditions to coexist and/orimprove system performance. Some of such separate devices may becontrolled directly by intelligent configuration unit 446, which, inthis example, further includes control and communication interfaces (notshown) to extract and send information to the separate devices thatenable the direct manipulation of incoming optical signals 444. Suchseparate devices are alternatively controlled by indirect communicationwith intelligent configuration unit 444, for example, through a controlchannel (not shown). In some embodiments, intelligent configuration unit446 is combined with separate multiplexers, aggregators, and/orcombiners in an integrated structure.

In an exemplary embodiment, ODC 404 includes a wavelength filter 446,which is implemented for downstream transmission to efficientlytransition from the single fiber-multiple wavelength medium (i.e.,downstream long fiber 408) between optical hub 402 and ODC 404, to themultiple fiber/single wavelength per fiber environment (i.e., shortfibers 412) between ODC 404 and the respective termination devices ofend users 406. Wavelength filter 446 may include, for example, awavelength-division multiplexing (WDM) grating, and/or a cyclic arrayedwaveguide grating (AWG). In the exemplary embodiment, ODC 404 furtherincludes a downstream optical switch 448, which utilizes a controlsignal from intelligent configuration unit 442 to transmit the outputfrom wavelength filter 446 along downstream short fibers 412. Whereupstream transmission is optionally desired, ODC 404 further includes anoptical combiner 450 to aggregate signals from the many upstream shortfibers coming from the optical end devices of end users 406, to a singlefiber (i.e., upstream long fiber 410) at ODC 404. Optical combiner 450may include a WDM grating or splitter. In this configuration, ODC 404further may include an upstream optical switch 452 between short fibers412 and optical combiner 450, which together function to combine thedifferent upstream optical carrier into a single upstream heterogeneouswavelength multiplexed signal, in coordination with the wavelengthspacing and tuning processes of intelligent configuration unit 442,described further below. This aggregate upstream heterogeneous signal iscarried over upstream long fiber 410 from ODC 404 to optical hub 402.

In an exemplary embodiment, data streams within optical hub 402 areassociated for the purpose of reception/transmission from/to thedifferent optical downstream transmitters 418, 420, 422 and upstreamreceivers 430, 432, 434, which are in communication with or connected tospecific ODCs throughout the area optical hub 402 serves (see also FIG.3, above). In this embodiment, intelligent configuration unit 442 isconfigured to utilize the known capability and configuration ofwavelength filter 446 (WDM grating or demultiplexer) to furtherconfigure optical signal parameters, such as wavelength, bandwidth,modulation type, etc., of downstream transmitters 418, 420, 422, inorder to reach specific target subscribers (i.e., end users 406).

In an alternative embodiment, downstream optical switch 448 isoptionally an N×N optical switch, and intelligent configuration unit 442is further configured to transmit control messages to downstream opticalswitch 448 to associate specific ports (not shown) with specificperformance characteristics and signal types to target subscribers,thereby providing significant flexibility in the type of service andwavelength system 400 can dedicate to a particular target subscriber. Inan alternative embodiment, where cost considerations are of greaterconcern, the N×N switch may be sized such that it covers only particularsubscribers (e.g., a business) that require greater flexibility inadjusting parameters. Residential subscribers, for example, may be fixedto a specific wavelength assignment and service configuration.

In this embodiment, for the reverse transmission direction, upstreamsignal flow is controlled by intelligent configuration unit 442 so thatthe appropriate wavelength is routed to the appropriate receiver type(e.g., upstream receivers 430, 432, 434) in optical hub 402. Incontrast, conventional optical nodes each serve only one signal type,and may not further function to manipulating or route signal trafficbased on wavelength or signal type. For such conventional nodes, thecharacteristics of the transmitted signal are typically fixed based onthe intended service. Accordingly, the signal processing in the upstreamdirection is substantially equivalent to the signal processing in thedownstream direction, but in reverse. For example, for each command ODC402 receives from intelligent configuration unit 442 for downstreamtransmission, intelligent configuration unit 442 may generate acounterpart command intended for upstream transmission. In an optionalembodiment, upstream transmission aggregates channels utilizing apassive combiner (not shown) instead of a wavelength multiplexer.

In an exemplary embodiment, fiber communication system 400 may befurther configured to include and implement an optical frequency combgenerator (not shown) for generating at least one coherent tone pair foreach coherent optical signals 444(3), which is then multiplexed withinintelligent configuration unit 442, or by a separate device (describedabove) in communication with intelligent configuration unit 442, priorto transmission over downstream long fiber 408 to ODC 404. Thisexemplary architecture and processing are described in greater detail inco-pending U.S. patent application Ser. No. 15/283,632, filed Oct. 3,2016, which is incorporated by reference herein.

Implementation of the embodiments described herein is useful formigrating hybrid fiber-coaxial (HFC) architectures towards other typesof fiber architectures, as well as deeper fiber architectures. TypicalHFC architectures tend to have very few fiber strands available from ODCto hub (e.g. fibers 408, 410), but many fiber strands could be deployedto cover the shorter distances that are typical from legacy HFC nodes toend users (e.g., fiber optics 412). In the exemplary embodimentsdescribed herein, two fibers (i.e., fibers 408, 410) are illustratedbetween optical hub 402 and ODC 404, which can include one or morelegacy HFC fiber nodes. That is, one fiber (i.e., downstream fiber 408)is utilized for downstream signal, and another fiber (i.e., upstreamfiber 410) is utilized for upstream signal. By utilization of theadvantageous configurations herein, fiber deeper or all-fiber migrationschemes can greatly minimize the need for fiber retrenching from an ODCor an HFC node to an optical hub. As described above, although twofibers (i.e., fibers 408, 410) are illustrated in FIG. 4, the presentsystems and methods may also be implemented utilizing only a singlefiber, with the utilization of additional optical circulators andwavelength management, for example as described further below.

Whereas the conventional fiber access network architecture transmitsonly analog signals through the conventional mode, the advantageousarchitecture disclosed herein, through implementation of an intelligentconfiguration unit and an ODC, is capable of additionally transmittingdirect and coherent optical signals simultaneously over the same longfiber based on available signal bandwidth occupancy, as disclosedfurther below with respect to FIGS. 6-10. This novel architecture andprocessing method is therefore particularly optimized for a cableenvironment desiring to reuse long fibers from a hub to a node. Theembodiments described herein may also be adapted to a remote PHYsolution, a remote cable modem termination system (CMTS) that isincluded in the fiber node, a coherent and non-coherent DWDM-PONarchitecture, a non-coherent IM-DD architecture, and/or intradyne,homodyne, and heterodyne coherent detection schemes in a long system.

In an exemplary embodiment, fiber communication system 400 is configuredto further implement wavelength tuning and selectable fixed wavelengths.Specifically, the various optical sources that become optical signals444 will optimally have either the capability of wavelength tuning, orfor fixed optical wavelength sources, the sources can be selected suchthat the sources may be implemented according to the allocation andoptimization criteria described herein. As discussed above, conventionalnetworks typically have few spare fibers between the optical hub and thelegacy node. Accordingly, one fiber is presumed to be available fortransmission in the downstream direction, and one fiber is presumed tobe available in the upstream direction, both typically covering tens ofkilometers distance from hub to node. The requirement to use only asingle fiber for each of downstream and upstream transmission does notpermit fiber retrenching between the hub and the node. According to thenovel systems and methods disclosed herein, however, new fiberinstallation need only be implemented over the significantly shorterdistances (e.g., short fibers 412) between the ODC, legacy HFC fibernodes, deeper nodes, end devices at businesses, and/or base stations orhomes (in case of fiber to the home architectures). Such new fiberextensions would typically span no more than a few thousand meters.According to this novel architecture, a legacy HFC fiber node can beeffectively converted into an ODC where many fiber segments originatetowards these new optical termination devices or optical end devices.

In an exemplary embodiment, the access network fiber topology of system400 implements signals from sources including, without limitation:analog modulated optical carriers such as the subcarrier multiplexedchannels used in cable; baseband digital modulated signals using directdetection mechanisms such as non-return-to-zero (NRZ), return-to-zero(RZ), pulse amplitude modulation (PAM), including PAM4 and PAM8;differential detection signals such as differential phase-shift keying(DPSK) and differential quadrature phase-shift keying (D-QPSK); coherentmodulated optical signals such as binary phase-shift keying (BPSK),quadrature phase-shift keying (QPSK) and higher order quadratureamplitude modulation (QAM); and polarization multiplexing transmissiontechniques for coherent modulation.

In further operation within the environment of fiber communicationsystem 400, wavelengths of respective components are subject to changeunder different conditions. In some situations, where any two signalwavelengths get close enough to each other, a level of interferencebetween the respective signals may increase. Where two such signalwavelengths lay on top of each other, optical beat interference may alsobe experienced. In an exemplary embodiment, laser diodes may beimplemented, which are configured to have temperature control and/orfrequency tuning control (T/F Ctrl) capabilities to maintain signalwavelengths such that they may be separated at specific desired spacingwithin certain tolerance values. According to an exemplary embodiment offiber communication system 400, at least one laser diode is implementedfor each respective transmitter and receiver within the network. In anembodiment, at least two long fibers (e.g., long fibers 408, 410) arerequired for N subscribers (e.g., end users 406) using N wavelengths.Alternatively, a single fiber could be used for N subscribers using 2Nwavelengths, that is, N downstream wavelengths and N upstreamwavelengths.

FIG. 5 is a schematic illustration of an alternative fiber communicationsystem 500. Fiber communication system 500 is similar to fibercommunication systems 300 (FIG. 3) and 400 (FIG. 4), except that fibercommunication system 500 utilizes wavelength filtering and injectionlocking techniques, which are also described in greater detail inco-pending U.S. patent application Ser. No. 15/283,632, as discussedabove. Fiber communication system 500 includes an optical hub 502, anODC 504, and end users 506. Optical hub 502 communicates with ODC 504through downstream long fiber 508 and upstream long fiber 510. ODC 504communicates with end users 506 through short fibers 512. Forsimplification of explanation, deep nodes and cable (e.g., coaxial) arenot shown, but may be implemented along the signal path of short fibers512 similarly to the embodiments described above with respect to FIGS. 3and 4.

Optical hub 502 includes a downstream transmitting portion 514 and anoptional upstream receiving portion 516. In an exemplary embodiment,downstream transmitting portion 514 includes at least two of an analogdownstream transmitter 518, a polarization multiplexed IM-DD downstreamtransmitter 520, and a coherent downstream transmitter 522. End users506 are comparable to end users 308 (FIG. 3) and end users 408 (FIG. 4),and may, for example, include one or more downstream termination units.In the exemplary embodiment, end users 506 include at least two of ananalog downstream receiver 524, a polarization multiplexed IM-DDdownstream receiver 526, and a coherent downstream receiver 528. Whereupstream communication is optionally desired (i.e., through upstreamlong fiber 510), upstream receiving portion 516 includes at least two ofan analog upstream receiver 530, a polarization multiplexed IM-DDupstream receiver 532, and a coherent upstream receiver 534. In thisexemplary embodiment, end users 506 include at least two of an analogupstream transmitter 536, a polarization multiplexed IM-DD upstreamtransmitter 538, and a coherent upstream transmitter 540. A polarizationmultiplexed IM-DD link is illustrated in the exemplary embodiment ofFIG. 5. Nevertheless, the present systems and methods may be implementedutilizing a subset link that is not polarization multiplexed. Theinjection locking techniques described herein advantageously allow forthe novel combination of polarization multiplexing with IM-DD.

In operation, optical hub 502 further includes an intelligentconfiguration unit 542, comparable to intelligent configuration units318 (FIG. 3) and 442 (FIG. 4), and may be a standalone or integrateddevice having multiple functionalities, or a separate device incommunication with other devices serving to multiplex, aggregate, and/orcombine various signals. Intelligent configuration unit 542 workscooperatively with ODC 504 such that ODC 504 may demultiplex theheterogeneous signal types from one another to be separately transmittedover short fibers 512 to particular end users 506 capable of receivingthat type of signal.

In an exemplary embodiment of fiber communication system 500, furtherincludes a seed generator 544 and a wavelength filter 546. Wavelengthfilter 546 may include, for example, a WDM grating. In operation,wavelength filter 546 serves to support injection locking of laserdiodes implemented within the various respective transmitters andreceivers of the network. In an exemplary embodiment, the variousoptical sources represented by transmitters 518, 520, 522 includeinjection locked lasers that are modulated using different formats, andthe master source (not shown) for injection locking is a multi-tonegenerator of high spectral purity (narrow linewidth), as described inco-pending U.S. patent application Ser. No. 15/283,632, discussed above.In an alternative embodiment, other or additional optical sources couldbe implemented, including, but not limited to, broadband wavelengthsources. Implementation of the narrow linewidth source described hereinadvantageously allows for a significantly diversified set of modulationformats, including coherent optical modulation.

According to the embodiment illustrated in FIG. 5, wavelength filtersmay be advantageously implemented to separate multi-tone optical signalsinto individual wavelengths to injection lock the lasers. Additionally,the multi-tone sources may be placed in different locations. In anexemplary embodiment, in order to minimize complexity in thedistribution portion of the network, a multi-tone source is disposed inwithin optical hub 502 near to where the downstream signals originate.In an exemplary embodiment, ODC 504 further includes a demultiplexingwavelength filter 548 and a multiplexing wavelength filter 550. Filter548 may, for example, include a cyclic arrayed waveguide grating (AWG),and filter 550 may, for example, include a WDM grating or splitter.

Similar to the embodiment illustrated in FIG. 4, the access networkfiber topology of fiber communication system 500 implements signals fromsources including, without limitation: analog modulated optical carrierssuch as the subcarrier multiplexed channels used in cable; basebanddigital modulated signals using IM-DD mechanisms such as NRZ, RZ, PAM4,and PAM8; differential detection signals such as DPSK and D-QPSK;coherent modulated optical signals such as BPSK, QPSK, and higher orderQAM; and polarization multiplexing transmission techniques for coherentmodulation and non-coherent modulation, as shown in the IM-DDconfigurations illustrated in FIG. 5.

In an alternative embodiment, fiber communication system 500 is furtherconfigured to implement coherent links by leveraging the high spectralpurity of a common injection locking source (not shown) received by twodifferent lasers, but where one of the round trip paths to a laser isshifted in phase by 90 degrees. This phase shifting generates the I andQ paths needed for a coherent QAM modulated signal using two directlymodulated laser diodes. This technique can be expanded to twopolarizations with 4 directly modulated laser diodes thereby achievingpolarization multiplexing, as described in co-pending U.S. patentapplication Ser. No. 15/283,632, discussed above. In a furtheralternative embodiment, polarization multiplexing may be achievedthrough utilization of at least two direct detect links that share acommon injection locking source. The resulting two injection lockedtransmitters can thus be polarization multiplexed once so synchronizedthrough the common injection locked source. In this embodiment, theintensity modulation of light described here can be achieved throughdirect modulation of laser diode current. However, the present systemsand methods may also utilize other intensity modulation techniques, suchas electro-optical and electro-absorption intensity modulationtechniques using external modulators.

Fiber communication system 500 differs from fiber communication system400 system 500 is advantageously capable of avoiding use of temperaturecontrol or frequency control mechanisms, due to the fact that the novelfiltering techniques of system 500, as well as the generation of equallyspaced multi-tones, serves to restrict lasing to a fixed spacing betweenwavelengths. Systems and methods according to this embodiment furtheradvantageously also results in the elimination of optical beatinterference. System 500 further differs from system 400 in that, wheresystem 400 utilizes two fibers for N subscribers that fully use thefiber spectrum, system 500 utilizes unmodulated optical carriers forinjection locking which use half of a single fiber spectrum. Therefore,in this example, with two fibers available, one half of a one fiberspectrum is used for downstream data, one half of one fiber spectrum isused for upstream data, one half of one fiber spectrum is used forunmodulated optical carriers, and the remaining half of the fiberspectrum of the two fibers is not used. Accordingly, if three fibers areutilized, an entire spectrum of a first fiber may be used for downstreamdata transmission, an entire spectrum of a second fiber may be used forupstream data transmission, and an entire spectrum of the third fibermay be used for unmodulated optical carriers. Thus, to carry N opticalcarriers with the same bandwidth, system 400 would need two opticalfibers, whereas system 500 would need three optical fibers. In thisexample, system 500 is less efficient than system 400; however, thelaser diodes (not numbered) utilized by end users 506 are not requiredto be wavelength-specific, thereby resulting in significantly lowercapital and operating expenditures throughout system 500.

In a further alternative embodiment, the present inventors contemplatehybrid approach to implement principles of systems 400 and 500 together,including, without limitation, a wavelength filtered architecture wheresome of the optical sources are wavelength-tuned or of a fixedwavelength to fit within a filtered channel. In such a hybrid system,the seed optical signal to injection lock the optical transmitter may beavoided for at least a portion of the optical links. In an exemplaryembodiment of this alternative, some optical signals will be capable ofwavelength tuning and others will have fixed wavelengths requiringoperator knowledge of the wavelength and signal format to optimizeperformance, and/or wavelength filtering is implemented utilizinginjection locking techniques.

FIGS. 6A-6D illustrate an exemplary process 600 for successivewavelength placement of heterogeneous optical signals in accordance withan exemplary embodiment of the present disclosure. Process 600implements an intelligent wavelength mapping approach (e.g., by anintelligent configuration unit according to the above-describedembodiments) of optical signals over the wavelength transmission windowof a fiber. In an exemplary embodiment, process 600 includes one or morealgorithms for optical signal wavelength allocation and configurationoptimization, and includes methodology regarding how a fiberinfrastructure is optimized to achieve capacity, robustness, and otherperformance targets based on one or more of optical link resources andcomponent characteristics, optical channel conditions, and thetransmission requirements.

Process 600 provides for one or both of wavelength mapping andwavelength allocation for the different optical links, having differentmodulation formats and detection schemes, to meet traffic servicerequirements of the fiber infrastructure. Process 600 advantageouslyallows an optical hub to significantly increase the volume ofheterogeneous signals that can be transmitted over available fiberspectral resources. Process 600 is organized such that, when implementedby a processor (e.g., processor 324, FIG. 3), an intelligentconfiguration unit is able to gather information on components used,types of optical links, and types and characteristics of thearchitecture within the fiber communication system. For example, process600 is configured to determine whether a particular signal isrepresented by a tunable wavelength, a fixed wavelength, or a filteredwavelength or a hybrid architecture.

In an exemplary embodiment, process 600 is further configured toleverage one or more of the following optical carrierparameters/characteristics: individual carrier power levels; aggregatecarrier power; number of optical carriers; wavelength spacing amongcarriers; modulation format used; carrier configurability; and carriertunability. Process 600 may be further configured to additionally takeinto consideration one or more of the following fiber environmentcharacteristics: type of fiber; amplification and/or loss devices (e.g.,an EDFA); wavelength filters or splitters; and fiber distributionnetwork topology. Additionally, process 600 may still further considerthe measurement and classification of fixed-wavelength andunknown-wavelength laser diodes in order to determine a correctwavelength bin. The size of a wavelength bin, for example, may beaffected by an assessment of temperature, age, or power variability. Inan exemplary embodiment, a wavelength is presumed to stay within adetermined wavelength bin when the wavelength is deemed to becontrollable.

In an optional embodiment of process 600, depending on the modulationformat used, target optical signal to noise ratio (OSNR) requirementsfor different optical signals are calculated in advance and generatedinto a lookup table, which may then be utilized during implementation ofprocess 600 to control and minimize the optical power of each opticalcarrier, and also to adjust optical power of a carrier when noise levelincreases due to non-linear effects/interactions among the severalcarriers. Such non-linear effects may include self-phase modulation(SPM), cross-phase modulation (CPM), and/or four-wave mixing (FWM). Theeffects of SPM and CPM are more pronounced on signals with highermodulation bandwidths. The effects of FWM and CPM are more pronouncedwith narrower/decreased channel spacing of wavelengths. The effects ofFWM are also more pronounced with signals having lower chromaticdispersion. FWM is therefore of particular concern with spread signals.

Furthermore, noise assessment may depend not only on the type of source,but also on whether direct or external modulation is used, as well asany introduction of noise by devices such as amplifiers, such as noisefrom an EDFA, or amplified spontaneous emission(ASE)/superluminescence).

FIG. 6A illustrates a graphical representation of an initial wavelengthplacement according to process 600. According to an exemplaryembodiment, this initial placement is represented by an optical signalintensity 602 (y-axis) over a wavelength spectrum 604 (x-axis) of thefiber for a plurality of analog carrier signals 606(1), . . . 606(N).Placement of analog carrier signals 606 (also referred to as carriers orcarrier waves) may occur, for example, after an initial assessment ofthe optical link resources and characteristics of the network topology.

In the exemplary embodiment, analog carriers 606 are chosen for initialplacement because they represent fixed wavelength optical carriers, andmay include analog modulated links carrying their respective signals athigh power levels due to high signal to noise ratio (SNR) requirements.Analog carrier signals are typically not tunable, but are often thelargest contributors of noise over wavelength spectrum 604. Analogcarrier signals include high linearity requirements, and are consideredto be less flexible than other signals. Analog transmitters (e.g.,transmitters 418 (FIG. 4), 518 (FIG. 5)), however, can be set atparticular frequencies. Accordingly, transmission frequencies are chosenfor analog carrier signals 606 such that carriers 606 are spread wideacross wavelength spectrum 604 before consideration of other signals ofdifferent types.

Once process 600 verifies that the power level of analog signals 606 isoptimized, their noise level deemed acceptable, and that the severaloptical carriers are properly spaced apart without interference from oneanother, process 600 places the next signal in the successive wavelengthplacement scheme. Optionally, before placing additional signals, process600 may first calculate noise (not shown) across wavelength spectrum 604based on the placement of the optical carriers of analog carrier signals606, in order to more optimally place additional carriers in appropriateavailable wavelengths within wavelength spectrum 604.

FIG. 6B illustrates a graphical representation of successive wavelengthplacement of heterogeneous optical signals according to process 600following the initial wavelength placement illustrated in FIG. 6A.

In the exemplary embodiment, robust optical carriers are next chosen forplacement within portions along wavelength spectrum 604 that experiencethe worst noise conditions, that is, relatively near to or adjacent theplacement of analog carrier signals 606. In the example of FIG. 6B,first NRZ optical carriers 608(1), . . . 608(N′) are chosen for thissecond level of placement because they represent direct modulated/directdetection optical link carriers which can be adjusted in power so thatthe NRZ transmissions operate at an optimum target performance withinpredetermined appropriate margins.

NRZ optical carriers 608 are suited to fill the spectrum adjacent analogcarriers due to the “forgiving” nature of an NRZ signal. That is, firstNRZ optical carriers 608 are considered to have among the lowest SNR andthe highest noise tolerance of the heterogeneous signals, and areadditionally quite tolerant of the non-linear components generated byadjacent signals (i.e., analog carriers 606) along wavelength spectrum604. In an exemplary embodiment, first NRZ optical carriers 608 areplaced to effectively border the portion of wavelength spectrum aroundeach analog carrier signal 606. Alternatively, QPSK signals havecomparable carrier characteristics, and may be placed adjacent analogcarrier signals 606 in place of first NRZ optical carriers 608. A pocket609 is thereby formed between adjacent first NRZ optical carriers 608,which represents an area of relatively low noise within wavelengthspectrum 604.

After placement of robust first NRZ optical carriers 608, process 600may optionally recalculate noise across wavelength spectrum 604 to bothaccount for the addition of the new optical carriers (i.e., first NRZoptical carriers 608), and to more optimally identify pocket 609 forplacement of signals within wavelength spectrum 604 that have higher SNRrequirements.

FIG. 6C illustrates a graphical representation of further successivewavelength placement of heterogeneous optical signals according toprocess 600, following the wavelength placement illustrated in FIG. 6B.In the exemplary embodiment, optical signals having higher OSNRrequirements are next chosen for placement within pocket 609 (andsimilar regions of relatively low noise), and spaced from the placementof analog carrier signals 606. In the example of FIG. 6C, PAM4 opticalcarriers 610(1), . . . 610(N″), 16QAM optical carriers 612(1), . . .612(N″), and 64QAM optical carriers 614(1), . . . 614(N″″) are chosenfor this third level of placement because they represent relatively highSNR optical link carriers which generally are tunable, but requirepremium areas of low noise within wavelength spectrum 604. In theexemplary embodiment illustrated, 16QAM optical carriers 612 may requirea lower SNR than 64QAM optical carriers 614, for example, but will stillrequire a significantly higher SNR than first NRZ optical carriers 608.According to the exemplary embodiment, 16QAM optical carriers 612 and64QAM optical carriers 614 may represent either coherent or digitalcarriers.

After placement of the higher SNR optical carriers 610, 612, and 614,process 600 may again optionally recalculate noise across wavelengthspectrum 604, as well as the non-linear effects across the differentcarriers, to account for the addition of the newly placed opticalcarriers. According to this optional embodiment, the power level on someof the optical carriers may be further adjusted in the event that theparticular SNR requirements for the intended modulation format of aspecific carrier is not satisfied. After such power adjustment,non-linear distortion and noise impact may then be recalculated.

FIG. 6D illustrates a graphical representation of a final successivewavelength placement of heterogeneous optical signals according toprocess 600, following the wavelength placement illustrated in FIG. 6C.In the exemplary embodiment, the remaining more robust, but generallylower power level, carriers are inserted into the remaining availableportions of wavelength spectrum 604. In the example of FIG. 6D, QPSKoptical carriers 616(1), . . . 616(N′″″) and second NRZ optical carriers618(1), . . . 618(N′) are chosen for this fourth level of placementbecause they represent generally tunable and tolerant carriers havinglower SNR requirements then the less tolerant carrier signals added asillustrated in FIG. 6C.

As described above, NRZ and QPSK carrier signals have some comparablecharacteristics with respect to robustness and SNR requirements, and maybe substituted for each other (or mixed) in the second and fourthplacement levels described herein, depending on particular signalcharacteristics such as symbol rate, baud rate, etc. Process 600 with usis configured to optimally choose the robust optical signals to add intowavelength regions having suboptimal noise levels, and according tomeasured and/or monitored signal and fiber characteristics. Once all ofthe optical carrier signals are so placed, non-linear effects and noiseimpact may be optionally recalculated.

FIG. 7 illustrates an alternative graphical representation of a threedimensional wavelength placement 700, as compared with the final carrierplacement of process 600, depicted in FIG. 6D. In this exemplaryembodiment, wavelength placement 700 is represented by wavelengthspectrum 702 (x-axis), efficiency 704 (y-axis), and power 706 (z-axis),illustrating wavelength allocation with a fiber strand (not shown)following placement according to a performance optimization process oralgorithm, for example, process 600 (FIG. 6).

As described above, when a single carrier is the only signal occupying afiber strand, interactions with other carriers are not a concern. Suchsingle carrier fiber strands are limited chiefly by the amount of powerthat particular fiber can handle without exerting distortion ontoitself. A signal with lower SNR requirement will generally be morerobust than one with a higher SNR requirement, and when two or more suchsignals are present within the same fiber, interaction and interferencebetween the signals must be addressed.

In the exemplary embodiment, wavelength placement 700 is illustrated asa three dimensional consideration of various requirements regardingpower, SNR, efficiency, adjacent noise characteristics, and bandwidthoccupancy. In an alternative embodiment, different signal and/or fibercharacteristics, including, without limitation: modulation format;polarization multiplexing; channel coding/decoding, including forwarderror correction; fiber length; aggregate carrier power; number ofoptical carriers; wavelength spacing among carriers; carrierconfigurability; carrier tenability; fiber type; amplification and/orloss devices; wavelength filters or splitters; and fiber distributionnetwork topology. In an alternative embodiment, placement 700 may beoptimized in consideration of a number of these additionalconsiderations, thereby rendering placement 700 as a five or sixdimensional allocation placement, or greater.

FIG. 8 is a flow chart diagram of an exemplary optical signal wavelengthallocation process 800 that can be implemented with fiber communicationsystems 300, 400, 500, and complimentary to process 600, depicted inFIGS. 3-6, respectively, and described above. Process 800 represents oneor more subroutines and/or algorithms for optical signal wavelengthallocation and configuration optimization. In an exemplary embodiment,process 800 begins at step 802. In step 802 process 800 performs a fibersegment analysis subprocess, explained further below with respect toFIG. 9. After completing the fiber segment analysis, process 800proceeds to step 804. In step 804, process 800 performs a signalanalysis subprocess, explained further below with respect to FIGS.10A-C. After completing the signal analysis, process 800 proceeds tostep 806. In step 806, process 800 performs a spectrum assignmentsubprocess, explained further below with respect to FIG. 11. In anexemplary embodiment, the subprocess of step 806 may include, or becomplementary with, process 600, depicted in FIGS. 6A-6D. Uponcompletion of spectrum assignment of optical carriers, process 800proceeds to step 808. In an exemplary embodiment, step 808 ends process800. In an alternative embodiment, step 808 represents a return to step802, in order to repeat process 800 one or more times as desired.

FIG. 9 is a flow chart diagram of an exemplary fiber segment analysissubprocess 900 that can be implemented with allocation process 800depicted in FIG. 8. In an exemplary embodiment, subprocess 900 embodiesstep 802, FIG. 8, or may begin from a prompt or call from step 802.Subprocess 900 proceeds from start to step 902. In step 902, subprocess900 determines the type of fiber (e.g., long fiber 310, FIG. 3) utilizedto broadcast the heterogeneous signals. In an exemplary embodiment, thefiber type is SM-SMF28. Subprocess 900 then proceeds to step 904, wherethe length of the fiber is determined. In an exemplary embodiment, thelength is determined in kilometers. Subprocess 900 then proceeds to step906, where latitude and longitude information regarding the fiber aredetermined. In an exemplary embodiment, such information considers bothinput and output from the fiber segment, as well as information thatprecedes and follows the fiber segment.

In addition to the general fiber information, subprocess 900 analyzesfiber parameters in consideration of the spectral placement ofheterogeneous signals. For example, at step 908, subprocess 900determines the presence of at least one of dispersion, loss, andnon-linear model parameters for SPM, CPM, and FWM. In an exemplaryembodiment, other parameters may be considered, as discussed above withrespect to FIGS. 6-7. Subprocess 900 then determines whether the fiberincludes an amplifier or lost device at step 910. In an exemplaryembodiment, step 910 is a decision step. If an amplifier or lost device(e.g., EDFA/AMP) is included, step 910 proceeds to step 912, where thenoise is recorded from the amplifier/loss device. In an exemplaryembodiment, step 912 further records power range and/or a non-linearparametric description of the amplifier/loss device. Once recorded,subprocess 900 proceeds from step 912 and returns to process 800 (FIG.8), and to step 804 specifically. If no amplifier/loss devices includedat step 910, subprocess 900 proceeds directly from step 910 to step 804.

FIGS. 10A-C illustrate a flow chart diagram of an exemplary signalanalysis subprocess 1000 that can be implemented with allocation process800 depicted in FIG. 8. In an exemplary embodiment, subprocess 1000embodies step 804, FIG. 8, or may begin from a prompt or call from step804. In an alternative embodiment, subprocess 1000 may proceed directlyafter steps 910/912, FIG. 9, or simultaneously with subprocess 900.

Subprocess 1000 proceeds from start to step 1002. Step 1002 is a returnpoint from the several subroutines included within subprocess 1000,described further below. Step 1002 returns subprocess 1000 to step 1004.Step 1004 is a decision step. In step 1004, subprocess 1000 analyzes theheterogeneous signals to determine whether there are any unassignedoptical signals within the heterogeneous signal group. If step 1004determines that there is at least one unassigned optical signal,subprocess 1000 proceeds to step 1006. If step 1000 for determining thatthere are no further optical signals to assign along the spectrum,subprocess 1000 instead proceeds to step 1007 which builds the opticalcarrier list along with the characterizing parameters, and thus a returnto subprocess 800 (FIG. 8), and specifically to step 806.

Step 1006 is also a decision step. In step 1006, subprocess 1000determines whether the optical signal at issue is an analog signal. Ifstep 1006 determines that the optical signal is an analog signal,subprocess 1000 proceeds to step 1008, where the optical signal isassigned an analog signal ID. If, however, the optical signal is notdetermined to be an analog signal, subprocess 1000 proceeds to step1010. After an analog signal ID is assigned in step 1008, subprocess1000 proceeds to an analysis subroutine 1012. Analysis subroutine 1012begins at step 1014. Step 1014 is a decision step. In step 1014,analysis subroutine 1012 determines whether the wavelength of theassigned optical signal is fixed. If the wavelength is determined to befixed, analysis subroutine 1012 records the fixed wavelength at step1016 and proceeds to step 1018. If though, step 1014 determines that thewavelength is not fixed, subroutine 1012 records the granularity and therange of the signal in step 1020, and proceeds to step 1018.

Step 1018 is a decision step. In step 1018, analysis subroutine 1012determines whether external modulation is being utilized. If suchmodulation is determined to be utilized, analysis subroutine 1012records the external modulation, as well as laser diode parameters, ifany, at step 1022 and proceeds to step 1024. If though, step 1018determines that external modulation is not being utilized, subroutine1012 records the laser diode parameters in step 1026, and proceeds tostep 1024. Step 1024 is a decision step. In step 1024, analysissubroutine 1012 determines whether power at an input is fixed. If thepower is determined to be fixed, analysis subroutine 1012 records theinput power at step 1028, and proceeds to step 1030. If though, step1024 determines that the input power is not fixed, the power range atthe input is recorded at step 1032, and analysis subroutine 1012 thenproceeds to step 1030.

Step 1030 is a decision step. In step 1030, analysis subroutine 1012determines whether there is amplification being implemented in the fibersegment. If such amplification is determined to be implemented, analysissubroutine 1012 records the location, amplifier characteristics, andoutput signal power at step 1034 and proceeds to step 1036. If though,step 1030 determines that there is no amplification implemented in thefiber segment, subroutine 1012 proceeds directly to step 1036. Step 1036is a decision step. In step 1036, analysis subroutine 1012 determineswhether there is a discrete loss in the fiber segment. If a discreteloss is detected, analysis subroutine 1012 records the location,characteristics, and output power loss at step 1038, and proceeds tostep 1040. If though, step 1036 detects no discrete loss in the fibersegment, analysis subroutine 1012 then proceeds directly to step 1040.

Step 1040 exits analysis subroutine 1012. Once analysis subroutine 1012is completed, the modulation bandwidth and modulation format of theassigned analog signal are determined at step 1042. At step 1044, thenoise level is determined, as well as the maximum and minimum signallevels. At step 1046, subprocess 1000 determines the electrical SNRrequirements for the assigned analog signal. At step 1048, subprocess1000 calculates the optical SNR requirements for the assigned analogsignal, and then proceeds back to step 1002.

Referring back to step 1010, if subprocess 1000 does not detect ananalog signal in step 1006, subprocess 1000 then determines whether theoptical signal at issue is one of a digital direct detection opticalsignal and a differential detection optical signal. That is, step 1010is a decision step. If step 1010 determines that the optical signal is adirect or differential signal, subprocess 1000 proceeds to step 1050,where the optical signal is assigned a direct detection signal ID. If,however, the optical signal is not determined to be adirect/differential signal, subprocess 1000 proceeds to step 1052. Aftera direct detection signal ID is assigned in step 1050, subprocess 1000proceeds to an analysis subroutine 1054. Analysis subroutine 1054 issubstantially identical to analysis subroutine 1012, except the samesteps are performed for the direct/differential signal, as opposed to ananalog signal.

Once analysis subroutine 1054 is completed, the modulation bandwidth andmodulation format, as well as the symbol rate, of the assigneddirect/differential signal are determined at step 1056. In step 1058,the noise level is determined, as well as the maximum and minimum signallevels. At step 1060, subprocess 1000 calculates the optical SNRrequirements for the assigned direct/differential signal, and thenproceeds back to step 1002.

Referring back to step 1052, if subprocess 1000 does not detect adirect/differential signal in step 1010, subprocess 1000 then determineswhether the optical signal at issue is a digital coherent opticalsignal. That is, step 1052 is a decision step. If step 1052 determinesthat the optical signal is a coherent signal, subprocess 1000 proceedsto step 1062, where the optical signal is assigned a coherent signal ID.If, however, the optical signal is not determined to be a coherentsignal, subprocess 1000 returns to step 1002. After a coherent signal IDis assigned in step 1062, subprocess 1000 proceeds to an analysissubroutine 1064. Analysis subroutine 1064 is substantially identical toanalysis subroutines 1012 and 1054, except the same steps are performedfor the coherent signal, as opposed to an analog or direct/differentialsignal.

Once analysis subroutine 1064 is completed, the modulation bandwidth andmodulation format, as well as the symbol rate, of the assigneddirect/differential signal are determined at step 1066. In step 1068,the noise level is determined, as well as the maximum and minimum signallevels. At step 1070, subprocess 1000 calculates the optical SNRrequirements for the assigned coherent signal, and then proceeds back tostep 1002. The steps outlined above, particular steps need not beperformed in the exact order they are presented, unless the descriptionthereof specifically require such order.

FIG. 11 is a flow chart diagram of an exemplary spectrum assignmentsubprocess 1100 that can be implemented with allocation process 800depicted in FIG. 8. In an exemplary embodiment, subprocess 1100 embodiesstep 6, FIG. 8, or may begin from a prompt or call from step 806. In analternative embodiment, subprocess 1000 may proceed directly after step1007, FIG. 10A, or simultaneously with subprocesses 900 and 1000.

Subprocess 1100 proceeds from start to step 1102. Step 1102 analyzes theheterogeneous signal to identify the noise level each individual signalgenerates onto itself different power levels as a standalonetransmission. In step 1102, subprocess 1100 further determines themargin from SNR requirements for the lowest power level of operation. Instep 1104, subprocess 1100 identifies the number of optical signals asan aggregate, and by type of optical signal. In step 1106, subprocess1100 determines the approximate wavelength and granularity for eachassigned signal. In step 1108, subprocess 1100 places the fixedwavelength optical signals at lowest acceptable power levels in aprimary position (e.g., FIG. 6A), and then determines the noise levelsurrounding neighboring wavelengths. Once the fixed wavelength opticalsignals are placed, subprocess 1100 optionally updates the noise levelband map at step 1110.

Once the fixed wavelength optical signals are assigned, subprocess 1100then proceeds to step 1112, where optical signals are placed atrelatively lower acceptable power levels, but which require relativelybetter channel conditions, and which also will realize the greatestimpact on fiber resources (e.g., FIG. 6B), that is, apart from the fixedwavelength optical signals. In an exemplary embodiment, after the firsttwo optical signal placements are made, subprocess 1100 proceeds to step1114, where a subroutine 1116 is called to verify and/or adjust theOSNR.

Subroutine 1116 begins at step 1118. In step 1118, subroutine 1116calculates the noise levels introduced by the one or more opticalsignals at issue. In step 1120, subroutine 1116 determines non-linear,self-induced noise. In step 1122, subroutine 1116 determines non-linearnoise which may have been induced from other carriers. In step 1124,subroutine 1116 determines amplifier non-linear noise from all carriers.In step 1126, subroutine 1116 determines attenuator non-linear noisefrom all carriers. The preceding steps of subroutine 1116 may beperformed in the order listed, in a different order, or simultaneously.Once the noise in nonlinear components are determined, subroutine 1116proceeds to step 1128. Step 1128 is a decision step. In step 1128,subroutine 1116 determines whether the verified OSNR levels shouldwarrant an adjustment in power levels. If the power level adjustment iswarranted, subroutine 1116 returns to step 1118 and recalculates thenoise levels and determines nonlinear components as described above. Ifno power level adjustment is warranted, on the other hand, subroutine1116 completes, and returns to the step following the call to subroutine1116 (in this case, step 1130). In an alternative embodiment, subroutine1116 may be called at any point after placement of a particular opticalsignal.

In step 1130, a third placement of optical signals is performed (e.g.,FIG. 6C) to assign the spectrum for those signals that are consideredgenerally robust, and thus assign such signals in relatively closeproximity to those signals that impact fiber resources mostsignificantly. Once so assigned, subprocess 1100 proceeds to step 1132,which calls subroutine 1116. Once subroutine 1116 is completed,subprocess 1100 proceeds from step 1132 to step 1134. In step 1134, afourth placement of optical signals is performed (e.g., FIG. 6D) toassign the spectrum for those signals that require the next best channelconditions, relative to the previously assigned signals, in theremaining unoccupied channels that provide such optimum conditions. Inan exemplary embodiment of step 1134, placement of optical signals isperformed to avoid channel condition deterioration through clustering ofthis particular group of optical signals. Optionally, after step 1134,subprocess 1100 may perform an additional step 1136, in order to placeoptical signals that are considered a generally more robust relativelyclose proximity to those signals that impact fiber resources mostsignificantly. Once these optical signals are so placed, subprocess 1100proceeds to step 1138, where subroutine 1116 is again called, and afterwhich, subprocess 1100 returns to process 800 (FIG. 8), specificallystep 808.

FIG. 12 illustrates an alternative hybrid ODC 1200 that can beimplemented with fiber communication systems 300, 400, and 500, depictedin FIGS. 3, 4, and 5, respectively. In an exemplary embodiment, hybridODC 1200 includes an optical portion 1202 and an HFC portion 1204.Optical portion 1202 includes an architecture similar to ODC 404 (FIG.4) and ODC 504 (FIG. 5), as described above. HFC portion 1204 includesan architecture similar to deep nodes 306 (FIG. 3), also describedabove. As illustrated, hybrid ODC 1200 includes at least one HFC portion1204 within its integrated structure, but may include a plurality of HFCportions 1204 within the device structure, that is, portions 1202 and1204 are not separated by a material distance.

In the exemplary embodiment, hybrid ODC 1200 connects to an optical hub(e.g., optical hub 302, 402, or 502) by downstream long fiber 1206 andoptional upstream long fiber 1208. Hybrid ODC 1200 communicates withoptical transceivers 1210 of respective end users (e.g., end users 308,406, 506) through short fibers 1212. Similarly, hybrid ODC 1200communicates with an optical transceiver 1214 of HFC portion 1204through dedicated fibers 1216. Whereas short fibers 1212 may spandistances of up to several thousand feet, dedicated fibers 1216 may spana distance of less than a few feet to connect optical portion 1202 toHFC portion 1204 within an integrated device architecture. According tothis alternative structure, hybrid ODC 1200 includes at least one inputoptical interface 1218 for communication with the optical hub (not shownin FIG. 12), and one or more output electrical interfaces 1220 forcommunication with respective end users (not shown in FIG. 12) that arenot configured to directly receive and transmit optical signals. Forsimplicity of illustration, output optical interfaces to transceivers1210 are not shown. In some embodiments, transceivers 1210, 1214 mayinclude separate transmitters and receivers.

As illustrated in the exemplary embodiments depicted herein, a pluralityof differing optical signals (i.e., analog, direct, differential,coherent, etc.) may be intelligently monitored and assigned to besimultaneously over the same fiber segment, and without requiring anyretrenching of new fiber to transmit the differing, heterogeneouscarriers. For network environments having limited fiber resources,implementation of the present systems and methods significantlyincreases the ability (e.g., of an optical hub) to multiplex opticalsignals efficiently. Such fiber-optic distribution networksadvantageously realize the ability to utilize different coexistingoptical transport systems within the same network. Such differentoptical transport systems, even though coexisting based on a set ofconfiguration parameters, may nevertheless be selected through one ormore of the several processes, subprocesses, and algorithms describedherein that optimize signal placement based on the different performancemetrics.

Exemplary embodiments of fiber communication systems and methods aredescribed above in detail. The systems and methods of this disclosurethough, are not limited to only the specific embodiments describedherein, but rather, the components and/or steps of their implementationmay be utilized independently and separately from other componentsand/or steps described herein. Additionally, the exemplary embodimentscan be implemented and utilized in connection with other access networksutilizing fiber and coaxial transmission at the end user stage.

This written description uses examples to disclose the embodiments,including the best mode, and also to enable any person skilled in theart to practice the embodiments, including making and using any devicesor systems and performing any incorporated methods. The patentable scopeof the disclosure is defined by the claims, and may include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal language of the claims.

Although specific features of various embodiments of the disclosure maybe shown in some drawings and not in others, this is for convenienceonly. In accordance with the principles of the disclosure, a particularfeature shown in a drawing may be referenced and/or claimed incombination with features of the other drawings.

Some embodiments involve the use of one or more electronic or computingdevices. Such devices typically include a processor or controller, suchas a general purpose central processing unit (CPU), a graphicsprocessing unit (GPU), a microcontroller, a reduced instruction setcomputer (RISC) processor, an application specific integrated circuit(ASIC), a programmable logic circuit (PLC), a field programmable gatearray (FPGA), a DSP device, and/or any other circuit or processorcapable of executing the functions described herein. The processesdescribed herein may be encoded as executable instructions embodied in acomputer readable medium, including, without limitation, a storagedevice and/or a memory device. Such instructions, when executed by aprocessor, cause the processor to perform at least a portion of themethods described herein. The above examples are exemplary only, andthus are not intended to limit in any way the definition and/or meaningof the term “processor.”

This written description uses examples to disclose the embodiments,including the best mode, and also to enable any person skilled in theart to practice the embodiments, including making and using any devicesor systems and performing any incorporated methods. The patentable scopeof the disclosure is defined by the claims, and may include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal language of the claims.

What is claimed is:
 1. An optical network communication system, comprising: an optical hub including an intelligent configuration unit configured to monitor and multiplex at least two different optical signals into a single multiplexed heterogeneous signal; an optical distribution center configured to individually separate the at least two different optical signals from the multiplexed heterogeneous signal; at least one fiber segment connecting the optical hub and the optical distribution center, the at least one fiber segment configured to receive the multiplexed heterogeneous signal from the optical hub and distribute the multiplexed heterogeneous signal to the optical distribution center; and at least two end users, each including a downstream receiver configured to receive one of the respective separated optical signals from the optical distribution center.
 2. The system of claim 1, wherein the intelligent configuration unit comprises a processor and a memory, and an optical multiplexer.
 3. The system of claim 2, wherein the intelligent configuration unit further comprises an optical multiplexer.
 4. The system of claim 2, wherein the intelligent configuration unit further comprises at least one of a control interface and a communication interface to receive from and send information to an optical multiplexer.
 5. The system of claim 1, wherein the optical distribution center comprises a node optical demultiplexer configured to demultiplex the multiplexed heterogeneous signal.
 6. The system of claim 1, wherein the optical hub comprises at least two downstream transmitters, each configured to transmit one of the at least two different optical signals, respectively.
 7. The system of claim 6, wherein each of the at least two end users further includes an upstream transmitter, wherein the optical distribution center further comprises a node optical multiplexer, and wherein the optical hub further comprises at least two upstream receivers configured to receive a different optical signal from different ones of the transmitters of the at least two end users, respectively.
 8. The system of claim 6, wherein the intelligent configuration unit is further configured to multiplex the at least two different optical signals from the at least two downstream transmitters.
 9. The system of claim 1, wherein the at least two different optical signals include two or more of an analog signal, an intensity modulated direct detection signal, a differential modulated signal, and a coherent signal.
 10. The system of claim 1, wherein the at least two end users comprise at least two of a customer device, customer premises, a business user, and an optical network unit.
 11. The system of claim 1, further configured to implement coherent dense wavelength division multiplexing with a passive optical network architecture.
 12. The system of claim 11, wherein the at least two end users include at least N subscribers, and wherein the system comprises at least two fiber segments for each N subscribers.
 13. The system of claim 1, further configured to implement wavelength filtering and injection locking.
 14. The system of claim 13, wherein the at least two end users include at least N subscribers, and wherein the system comprises at least three fiber segments for each 2N subscribers.
 15. A method of distributing heterogeneous wavelength signals over a fiber segment of an optical network, comprising the steps of: monitoring at least two different optical carriers from at least two different transmitters, respectively; analyzing one or more characteristics of the fiber segment; determining one or more parameters of the at least two different optical carriers; and assigning a wavelength spectrum to each of the at least two different optical carriers according to the one or more analyzed fiber segment characteristics and the one or more determined optical carrier parameters.
 16. The method of claim 15, further comprising, after the step of assigning, multiplexing the at least two different optical carriers to the fiber segment according to the respective assigned wavelength spectra.
 17. The method of claim 15, wherein the at least two different optical carriers include two or more of an analog signal, an intensity modulated direct detection signal, a differential modulated signal, and a coherent signal.
 18. The method of claim 15, wherein the fiber segment characteristics include one or more of fiber type, fiber length, implementation of amplification and/or loss devices, implementation of wavelength filters or splitters, and fiber distribution network topology.
 19. The method of claim 15, wherein the optical carrier parameters include one or more of individual carrier optical power levels, aggregate carrier power, number of optical carriers, signal wavelength, wavelength spacing among carriers, modulation format, modulation bandwidth, carrier configurability, channel coding/decoding, polarization multiplexing, forward error correction, and carrier tenability.
 20. An optical distribution center apparatus, comprising: an input optical interface for communication with an optical hub; an output optical interface for communication with one or more end user devices configured to process optical signals; a wavelength filter for separating a downstream heterogeneous optical signal from the input optical interface into a plurality of downstream homogenous optical signals; and a downstream optical switch for distributing the plurality of downstream homogeneous optical signals from the wavelength filter to the output optical interface in response to a first control signal from the optical hub.
 21. The apparatus of claim 20, wherein the wavelength filter comprises at least one of a wavelength division multiplexing grating and a cyclic arrayed waveguide grating.
 22. The apparatus of claim 20, wherein the downstream optical switch is an N×N optical switch configured to associate particular ones of the plurality of downstream homogeneous optical signals with respective ones of the one or more end user devices.
 23. The apparatus of claim 20, wherein the first control signal is received from an intelligent configuration unit disposed within the optical hub.
 24. The apparatus of claim 20, further comprising: an upstream optical switch for distributing a plurality of upstream homogeneous optical signals collected from the output optical interface in response to a second control signal from the optical hub; and an optical combiner for aggregating the distributed plurality of upstream homogenous optical signals into a heterogeneous upstream optical signal to the input optical interface.
 25. The apparatus of claim 24, wherein the optical combiner comprises at least one of a wavelength division multiplexing grating and a passive optical splitter.
 26. The apparatus of claim 24, wherein the upstream optical switch is an N×N optical switch.
 27. The apparatus of claim 24, wherein the second control signal is a counterpart command of the first control signal.
 28. The apparatus of claim 24, wherein the optical distribution center is configured to receive the first and second control signals separately from the input optical interface.
 29. The apparatus of claim 24, further comprising a hybrid fiber coaxial portion in communication with the output optical interface.
 30. The apparatus of claim 24, wherein the second control signal is received from an intelligent configuration unit disposed within the optical hub. 